Today, a father's legacy to his child. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

It's midnight. I'm just back from Dallas, where a very moving thing happened. But the story begins on March 18th, 1937. That day, 294 children and teachers died when a natural gas leak blew up the school in New London, Texas.

A gadget called the Peerless Gas Odorizer came out right after the explosion. It drips a smelly mercaptan liquid into gas lines. That makes gas leaks obvious. They can't sneak up on you the way one sneaked up on New London.

I was in Dallas to designate the earliest surviving odorizer as a National Mechanical Engineering Landmark. It's a childishly simple thing -- perfect in its simplicity. This one ran for fifty years. It ran the first 25 years without any maintenance. It made natural gas safe after the New London explosion.

So we made our speeches. Then the son of the inventor stepped up to receive the plaque. He's head of the Peerless Company now. All his life the firm has made odorizers as a sideline. There's very little profit in them.

But he didn't talk about that. Instead he told one story. He told how his father jumped in the car and drove to New London right after the explosion. He was gone three days. And here the man's voice caught. I glanced up. He was fighting to keep his composure. Whatever he had to say was costing him dearly.

For three days, his father had dug in the wreckage along with others. He found a live teacher here -- a not-yet-dead child there. For three days he sorted through the worst natural gas accident in history.

After three days the father returned. He got from his car, went straight to his children, and embraced them. The father was crying. First time he ever saw him cry -- last time too.

I learned afterward that the father died while the son was in college. Years later, he said, when he had children of his own, he understood that his father had wept with relief because those weren't his children in New London on March 18th, 1937.

So the son has kept making these perfect, and childishly simple, little machines down through his entire adult life. Machines that make little sense on his balance sheets.

No wonder that story was so hard for him to tell. The inventor had, for just a moment, bridged the terrible silence that lies between father and child. He built his love for his children into a machine that would preserve other children for their tongue-tied fathers. This son wept tonight because he knew his father had spoken his love -- in the directness, grace, and simplicity of that old machine.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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The inventors of the Peerless Gas Odorizer were Donald A. Sillers, Sr. and Alexander Clarke, Sr. The Chief Executive Officer of the Peerless Mfg, Co. is Donald A. Sillers, Jr. The Odorizer and its history are described in a 1992 ASME Brochure prepared for the designation of the device as a National Historic Mechanical Engineering Landmark. For more on the odorizer, see Episode 644.